diff --git src/wp-includes/rest-api.php src/wp-includes/rest-api.php
index 4b49ebfdcb..cf05448781 100644
--- src/wp-includes/rest-api.php
+++ src/wp-includes/rest-api.php
@@ -1226,7 +1226,7 @@ function rest_validate_value_from_schema( $value, $args, $param = '' ) {
 	if ( isset( $args['format'] ) ) {
 		switch ( $args['format'] ) {
 			case 'date-time':
-				if ( ! rest_parse_date( $value ) ) {
+				if ( ! empty( $value ) && ! rest_parse_date( $value ) ) {
 					return new WP_Error( 'rest_invalid_date', __( 'Invalid date.' ) );
 				}
 				break;
diff --git src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
index e53ff4b910..4ca94dd83f 100644
--- src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
@@ -1036,6 +1036,16 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 			}
 		}
 
+		// Sending a blank (null or empty string) date or date_gmt value resets date and date_gmt to their
+		// default values (`0000-00-00 00:00:00`).
+		if (
+			( isset( $request['date_gmt'] ) && '' === $request['date_gmt'] ) ||
+			( isset( $request['date'] ) && '' === $request['date'] )
+		) {
+			$prepared_post->post_date_gmt = null;
+			$prepared_post->post_date     = null;
+		}
+
 		// Post slug.
 		if ( ! empty( $schema['properties']['slug'] ) && isset( $request['slug'] ) ) {
 			$prepared_post->post_name = $request['slug'];
@@ -1881,13 +1891,13 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 			'properties' => array(
 				'date'         => array(
 					'description' => __( "The date the object was published, in the site's timezone." ),
-					'type'        => 'string',
+					'type'        => [ 'string', 'null' ],
 					'format'      => 'date-time',
 					'context'     => array( 'view', 'edit', 'embed' ),
 				),
 				'date_gmt'     => array(
 					'description' => __( 'The date the object was published, as GMT.' ),
-					'type'        => 'string',
+					'type'        => [ 'string', 'null' ],
 					'format'      => 'date-time',
 					'context'     => array( 'view', 'edit' ),
 				),
diff --git tests/phpunit/tests/rest-api/rest-posts-controller.php tests/phpunit/tests/rest-api/rest-posts-controller.php
index ba174c448e..9d0a97f324 100644
--- tests/phpunit/tests/rest-api/rest-posts-controller.php
+++ tests/phpunit/tests/rest-api/rest-posts-controller.php
@@ -2555,6 +2555,66 @@ class WP_Test_REST_Posts_Controller extends WP_Test_REST_Post_Type_Controller_Te
 		$this->assertEquals( $params['excerpt'], $post->post_excerpt );
 	}
 
+	/**
+	 * Verify that updating a post with a `null` date or date_gmt results in a reset post, where all
+	 * date values are equal (date, date_gmt, date_modified and date_modofied_gmt) in the API response.
+	 * In the database, the post_date_gmt field is reset to the default `0000-00-00 00:00:00`.
+	 *
+	 * @ticket 44975
+	 */
+	public function test_rest_update_post_with_empty_date() {
+		// Create a new test post.
+		$post_id = $this->factory->post->create();
+		wp_set_current_user( self::$editor_id );
+
+		// Set the post date to the future.
+		$future_date = '2919-07-29T18:00:00';
+		$request     = new WP_REST_Request( 'PUT', sprintf( '/wp/v2/posts/%d', $post_id ) );
+		$request->add_header( 'content-type', 'application/json' );
+		$params = $this->set_post_data(
+			array(
+				'date_gmt' => $future_date,
+				'date'     => $future_date,
+				'title'    => 'update',
+				'status'   => 'draft',
+			)
+		);
+		$request->set_body( wp_json_encode( $params ) );
+		$response = rest_get_server()->dispatch( $request );
+		$this->check_update_post_response( $response );
+		$new_data = $response->get_data();
+
+		// Verify the post is set to the future date.
+		$this->assertEquals( $new_data['date_gmt'], $future_date );
+		$this->assertEquals( $new_data['date'], $future_date );
+		$this->assertNotEquals( $new_data['date_gmt'], $new_data['modified_gmt'] );
+		$this->assertNotEquals( $new_data['date'], $new_data['modified'] );
+
+		// Update post with a blank field (date or date_gmt).
+		$request = new WP_REST_Request( 'PUT', sprintf( '/wp/v2/posts/%d', $post_id ) );
+		$request->add_header( 'content-type', 'application/json' );
+		$params = $this->set_post_data(
+			array(
+				'date_gmt' => null,
+				'title'    => 'test',
+				'status'   => 'draft',
+			)
+		);
+		$request->set_body( wp_json_encode( $params ) );
+		$response = rest_get_server()->dispatch( $request );
+
+		// Verify the date field values are reset in the API response.
+		$this->check_update_post_response( $response );
+		$new_data = $response->get_data();
+		$this->assertEquals( $new_data['date_gmt'], $new_data['date'] );
+		$this->assertNotEquals( $new_data['date_gmt'], $future_date );
+
+		$post = get_post( $post_id, 'ARRAY_A' );
+		$this->assertEquals( $post['post_date_gmt'], '0000-00-00 00:00:00' );
+		$this->assertNotEquals( $new_data['date_gmt'], $future_date );
+		$this->assertNotEquals( $new_data['date'], $future_date );
+	}
+
 	public function test_rest_update_post_raw() {
 		wp_set_current_user( self::$editor_id );